KR20010096759A - Active Current Drive Circuit of Organic Light Emitting Device - Google Patents

Abstract

An active current driving circuit of an organic light emitting device, the method comprising: a charging unit configured to control an input voltage by a switching controller to accumulate electric charges by a potential difference between an input voltage input and a predetermined reference voltage, and optionally an input voltage according to switching control Or a driving unit including two or more low voltage elements for controlling a current by applying a voltage of a charging unit, an organic light emitting element emitting light by current flowing through the driving unit, and applying a voltage to both ends of the driving unit Consists of a power supply for controlling the current and adjusting the brightness of the organic light emitting device, by connecting two or more low-voltage devices in series to properly distribute the voltage to the devices and the organic light emitting device to prevent damage to the device, The voltage applied to the power supply unit at the same time can achieve the effect of using a high-voltage device Since the range is widened given a lot of current flowing in the organic light emitting device can increase the brightness of the organic light emitting device.

Description

Active Current Drive Circuit of Organic Light Emitting Device

The present invention relates to a current driving circuit of an organic EL panel, and more particularly to an active current driving circuit of an organic light emitting element.

Recently, the display concept of replacing the conventional CRT has been rapidly developed, and various types of flat panel displays are coming out in terms of size and utility. In addition, a display similar to an integrated device has been developed in combination with an integrated field emitting tracsistor (FET) to realize a miniaturized screen such as a head mount display (HMD) that can be worn on the body. In addition to such miniaturization, more technology that can control colors close to natural colors is required, and integration and resolution have also emerged as a key to the success of development.

In order to increase the density in the silicon process, the interface of external devices using high voltages with FETs driven at low voltages needs to be economical and drive currents using low voltage devices.

1 is a driving circuit diagram of an organic light emitting diode (OLED) according to the prior art.

Q1 is a switching FET used for the gate input, which applies a voltage to the Q2 gate according to the switching to turn Q2 on or off to open and close the conduction path to regulate the input of Q2. When Q1 is turned on, when a certain amount of current flows from the source S2 to the drain D2 and the voltage applied to the OLED has a value between 3.5 V and 7.0 V, the OLED operates to emit light and the C1 capacitor Wow The charge is accumulated by the difference voltage of.

Therefore, the C1 capacitor preserves the charge accumulated when the Q1 is turned on, even when the Q1 is turned off, so that the gate voltage applied to the Q2 ( ) As it is, providing a voltage to turn on Q2. That is, Q2 is the gate voltage ( ), The current flowing between the source S2 and the drain D2 of Q2 is controlled. The controlled current flows through Q2 and the OLED to provide voltage distribution to operate at the operating point of Q2.

Considering this from the point of view of turning on and off Q2, when Q2 is turned on, the voltage between the source S2 and the drain D2 of Q2 is lowered, and the voltage applied to the OLED increases to increase the current.

When Q2 is off, the gap between source S2 and drain D2 of Q2 + Almost all of the voltage is applied, so that the OLED is hardly energized. At this time, + In order to control the operating region of 3.5V to 7.0V, the Q2 device is destroyed in the case of a 3.5V process transistor when Q2 is turned off.

2 is a basic OLED active driving circuit diagram with a clamp diode attached.

As shown in FIG. 1, in order to solve the problem of breakage of transistor Q2 when Q2 is turned off, drain D3 and gate G3 serving as diodes do not lower the drain D2 of Q2 below -0.7V. Clamp the connected Q3 to the drain D2 of Q2.

Assume that the voltage at is 2.6V and the transistor Q2 is operable at 3.3V. Then, when Q2 is off, the voltage applied to Q2 should be fixed so that the drain (D2) voltage of Q2 does not go below -0.7V so that it does not take 3.3V or more. That is, Q3 conducts the source S3 and drain D3 of Q3 when the drain D2 portion of Q2 falls below -0.7V so that the drain of Q2 does not go below -0.7V.

When Q2 is on, that is, when drain D2 of Q2 rises to a positive potential, reverse voltage is applied to drain D3 and source S3 of Q3 so that no current flows to Q3 and OLED does not emit light.

From an OLED standpoint, when the Q2 drain (D2) potential is greater than -0.7V, that is, when Q2 is on, the voltage applied to the OLED is high, so a lot of current flows and the OLED emits light. Then, when the potential of the Q2 drain D2 becomes less than -0.7V, that is, before Q2 is turned off and broken, Q3 is conducted and clamped to -0.7V. Then the voltage across the OLED As it is reduced to -0.7V, the voltage applied to the OLED is lowered so that less current flows and the OLED does not emit light.

At this time, If -0.7V is greater than 3.5V when the OLED starts emitting light, the light is emitted even when Q2 is turned off. therefore Should not be greater than 4.2V. Is 4.2V, when Q2 is completely turned on, the potential of the drain D2 of Q2 rises to a positive value. For example, when the voltage rises to 2.8V, a total of 7V voltage is applied to the OLED. When the source S2 of the drain D2 of the Q2 is basically about 1.0V, the source S2 of the transistor Q2 takes 3.8V. It will take 4.5V. This limits the use of transistors with 3.3V low voltage.

Therefore, if Q3 acting as a clamp diode is attached, the transistor is not damaged. Wow The range of voltage is limited.

The active current driving circuit of the organic light emitting diode according to the related art described above has the following problems.

First, when the transistor is turned off and the organic light emitting device does not emit light, the voltage across the transistor is increased so that the transistor having a low voltage is destroyed, so that a high voltage device must be used.

Second, there is a problem in that the voltage applied to the circuit is limited in order to make the voltage applied to the transistor constant when the transistor is turned off so that the transistor is not destroyed and the organic light emitting device does not emit light.

Third, since the voltage range of the circuit is limited, the voltage applied to the organic light emitting element when the transistor is turned on is small, thereby reducing the efficiency of luminance.

Accordingly, the present invention has been made to solve the above problems, and when the OLED does not emit light, the lower limit voltage of the transistor is fixed to protect the transistor, and at the same time, several transistors for low voltage are connected in series to operate the organic light emitting device. It is an object of the present invention to provide an active current driving circuit of an organic light emitting device that increases the range of voltage applied to a circuit so as not to.

1 is a driving circuit diagram of an organic light emitting diode (OLED) according to the prior art.

2 is an active driving circuit diagram of a basic organic light emitting diode (OLED) with a clamp diode according to the prior art;

3A and 3B are basic conceptual diagrams for an active driving circuit of an organic light emitting diode (OLED) using a transistor having a low voltage.

4 is an active driving circuit diagram of an organic light emitting diode (OLED) in which the basic concept of FIGS. 3A and 3B is implemented as a circuit.

5 using four FET devices Active driving circuit diagram of an organic light emitting element OLED when the

An active current driving circuit of the organic light emitting diode according to the present invention for achieving the above object is a switching control unit for controlling the input voltage, the electric charge by the potential difference between the input voltage and the predetermined reference voltage input by the switching control unit A charging unit configured to accumulate the light, a driving unit consisting of two or more elements to selectively adjust the current by applying an input voltage or a voltage of the charging unit according to the switching control, an organic light emitting element emitting light by the current flowing in the driving unit; And a first power supply unit configured to apply a voltage to both ends of the driving unit to control a current flowing in the driving unit and to adjust the luminance of the organic light emitting diode.

The elements of the driving unit are different from each other in saturation characteristics and are connected in series between the power supply unit, and the organic light emitting element is connected in series with the elements of the driving unit between the power supply unit, and the elements of the driving unit and the organic light emitting element The voltage supplied by the first power supply unit is distributed.

The lower end of the device in the drive unit directly connected to the switching control unit further comprises a device for limiting the lower limit voltage of the device, the device is composed of any one of a clamp diode or FET.

The charging unit includes two or more capacitors for applying a voltage to each element of the driving unit when the switching control unit is turned off, and a second power supply unit supplying the reference voltage to the last stage of the capacitors.

The capacitor is determined according to the characteristics of each device and the input voltage of the driving unit such that the elements of the driving unit are equally switched, and the switching control unit and the driving unit include CMOS field effect transistors (CMOSFETs).

An operation according to a feature of the present invention is to add a transistor having a low voltage to the active current driving circuit of the conventional organic light emitting device, a plurality of transistors having the low voltage by connecting the organic light emitting device in series with the organic light emitting device When the light does not emit light, the voltage applied to the transistor can be reduced to prevent breakage of the transistor and at the same time, the range of the limited voltage can be widened.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of an active current driving circuit of an organic light emitting diode according to the present invention will be described with reference to the accompanying drawings.

3 is a schematic diagram of a basic concept of preventing a high voltage from being applied to a transistor fabricated by a low voltage process.

The circuit diagram conceptually illustrates the interface of a light emitting device operating at a relatively high voltage, such as an OLED, with a FET fabricated for 3.3V.

The voltage across is set at 2.6V and clamped by diode D1 at -0.7V at bottom of resistor r1 by diode. Let voltage be 7.OV. Therefore, as shown in FIG. 3A, r1 is applied with a voltage of 3.3 V, and resistor r2 is applied with an OLED of 6.3 V.

From the point of view of resistance, the voltage is divided by the ratio of the resistance of the OLED and the resistance of r2, and at this time, the voltage applied to r2 as shown in FIGS. 3A and 3B does not exceed 3.3V even if the OLED is turned on and off. It is the starting point of the main concept.

First, as shown in FIG. 3A, the voltage applied to r1 is fixed at 3.3V. When the value of r2 is decreased, most of the voltage is applied to the OLED because the bulk resistance of the OLED is large, and the OLED emits light.

And, as shown in Fig. 3b, the voltage applied to r1 is fixed at 3.3V, and when the value of r2 is increased to R, which is a large resistance, and takes a value close to the bulk resistance of the OLED so that the OLED does not turn off and emits light, The voltage across resistor R and the OLED across are properly distributed. At this time, the voltage applied to the OLED Using the previous value, the resistance R is adjusted so that the OLED has the highest potential difference that can turn off the OLED. Using this basic idea, the voltage across resistor R should be less than 3.3V.

4 is a schematic diagram of a circuit of the basic concept of FIGS. 3A and 3B.

Implement resistor r1 shown in FIGS. 3a and 3b as Q2, r2 and resistor R as p-MOS Q4, add C2 and add negative voltage Apply.

Warms up Q1 Is entering the voltage value, the gate of Q4 Wow - It will have a value between. Ratio of C1 and C2 values The gate G4 voltage of Q4 is adjusted accordingly. When the gate voltage G4 is adjusted according to the ratio of the values of C1 and C2, the Q4 also follows the on and off tendency according to the on and off state of Q2. Will appear.

When Q2 is turned on, the potential of the drain D2 of Q2 is shifted toward the + 2.6V potential, thereby causing a potential difference between the Q4 gate G4 and the source S4 to turn on Q4. Accordingly, the drain D4 of Q4 rises to a positive value, so that a sufficient voltage can be applied to emit light at the maximum intensity of the potential applied to the OLED itself.

When Q2 is off, the potential of the Q2 drain D2 is lowered to drop to -0.7V clamped by Q3, where the gate G4-source S4 potential of Q4 is in the off state as in the case of Q2. Will come close.

It is conceivable that Q4 close to off is replaced with a large resistor R as shown in Fig. 3B. The resistance R close to the turn off of Q4 is similarly adjusted to the resistance of the threshold just before the light emission of the OLED to prevent the breakage of Q4 by adjusting the voltage applied to Q4 to 3.3 V or less by resistance distribution. As a result, Q4 is not broken when Q2 and Q4 are off, and the OLED does not emit light.

5 is the potential of the cathode Is an example of the low-voltage transistor driving circuit for the case of lowering.

As shown in FIG. 5, Q4, a voltage-distributing resistor transistor as shown in FIG. 4, is connected in series with Q4, Q5 and Q6, and the capacitance value is appropriately set. Warms up Q1 Is entering the voltage level, the gates of Q4, Q5 and Q6 Wow - It will have a value between. Ratio of C1, C2, C3, C4 values The gate G4 voltage of Q4 is adjusted accordingly. When the gate voltage G4 is adjusted, Q4, Q5, and Q6 follow the on and off tendency according to the on and off state of Q2, and this is represented by the decrease and increase of the resistance in terms of resistance. When Q2 is on, Q4, Q5, and Q6 are also turned on to decrease the resistance. When Q2 is off, Q4, Q5, and Q6 are also turned off to increase resistance.

In other words, Q4, Q5, and Q6 can be regarded as resistances. As shown in FIG. 4 where only transistor Q4 is present, when Q2 goes off and the OLED is not active, a transistor corresponding to the maximum voltage that transistor Q4 will not be damaged should be used. You should use a transistor with a voltage that will not destroy that much.

On the other hand, when Q2 goes off and the OLED does not work, by connecting multiple transistors with low voltages in series, such as Q4, Q5, and Q6, it is possible to widen the limited voltage range so that the OLED does not work. .

Further, when the transistors having a high voltage at the time of OFF are used in the same way, the number of transistors connected in series is smaller than the case where the transistors have the same number of voltages.

Therefore, the OLED is driven by driving current with a higher voltage range for the limited operating region as shown in FIG.

The OLED active current driving circuit according to the present invention as described above has the following effects.

First, the clamp diode and the transistor are used to divide the voltage appropriately to the transistor and the OLED to have an effect of widening the range of applied voltage.

Second, since the clamp diode and the transistors having a plurality of low voltages are connected in series to distribute the voltage appropriately to the plurality of transistors and the organic light emitting device, the effect of using a high voltage transistor can be obtained and at the same time, the range of applied voltage is widened. There is.

Third, since the voltage range is widened by connecting the plurality of low voltage transistors in series, a large amount of current flows to the organic light emitting device, thereby increasing the luminance of the organic light emitting device.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (10)

A switching controller for controlling an input voltage; A charging unit which accumulates electric charges by a potential difference between an input voltage input by the switching control unit and a predetermined reference voltage; A driving unit including two or more elements for selectively adjusting an electric current by selectively applying an input voltage or a voltage of a charging unit according to the switching control; An organic light emitting element emitting light by a current flowing in the driving unit; And a first power supply unit configured to apply a voltage to both ends of the driving unit to control a current flowing in the driving unit, and to adjust the brightness of the organic light emitting element. The active current driving circuit of claim 1, wherein the elements of the driving unit have different saturation characteristics and are connected in series between the first power supply unit. The active current driving circuit of claim 1, wherein the organic light emitting element is connected in series with the elements of the driving unit between the first power supply unit. 4. The active current driving circuit of claim 3, wherein the elements of the driving unit and the organic light emitting element share a voltage supplied by the first power supply unit. The active current driving circuit of claim 1, further comprising a device configured to limit a lower limit voltage of the device at a lower end of the device in the driving unit directly connected to the switching controller. 6. The active current driving circuit of claim 5, wherein the device is any one of a clamp diode and a FET. The method of claim 1, wherein the charging unit Two or more capacitors for applying a voltage to each element of a driving unit when the switching control unit is turned off; And a second power supply unit for supplying the reference voltage to a last stage of the capacitors. 8. The active current driving circuit according to claim 7, wherein the capacitor is determined according to the characteristics of each device and the input voltage of the driving unit such that the elements of the driving unit are equally switched. The active current driving circuit of claim 1, wherein the elements of the driver are field effect transistors (CMOSFETs). The active current driving circuit of claim 1, wherein the switching controller is a CMOSFET.